1. Field of Invention
The present invention relates to a bearing that provides an indication of speed without further sensors.
2. Description of Related Art
A bearing of this type is disclosed in British patent application GB-A-1 237 932. This publication discloses an electrical measurement apparatus using an inductive coupling arrangement between a static core and a rotating part to communicate a measurement signal from the rotating part to the static core.
A disadvantage of the known assembly is that it is only suitable to transmit signals from a rotating part to a stationary part. Often it is desirable to know e.g. the rotational speed of a bearing.
It is an object of the present invention to provide a bearing for contactless transmission of signals, which also provides an indication of the rotational speed of the bearing without requiring further sensors.
The bearing according to the present invention has the advantage that next to contactless transmission of (power or data) signals, it serves as a sensor for the rotational speed of the bearing, without needing any further sensors. The coupling between the first and second coil varies when the first part of the bearing rotates with respect to the second part, and hence the signal transmitted from the first coil to the second coil varies. Thus, next to transmitting energy and/or data from the first coil to the second coil and vice versa, this embodiment also allows to obtain a signal representing the relative (rotational) speed of the first part of the bearing with respect to the second part.
A further advantage of this bearing is that it is possible to exchange electrical signals with a circuit which is fixed on or to the rotary part of the bearing. It will be clear that the present invention is applicable to all types of bearings, such as sleeve bearings, ball bearings and roller bearings.
It is known to a person skilled in the art to exchange electrical signals with a circuit which is fixed on a rotary shift with the aid of, for example, assemblies of slip rings and contacts. The disadvantage is that the slip rings and the contacts on the rotary shaft are subject to wear and that the electrical connections are less reliable. Moreover, the slip rings give rise to additional friction, which is not always desirable. The slip rings and contacts also take up additional space, which can be disadvantageous in some applications.
With the aid of the bearing according to the present invention it is possible to produce a reliable and friction-free coupling with a circuit fixed on the rotary shaft.
According to a preferred embodiment of the present invention, the axes of the first and of the second coil are coincident with the axis of rotation of the bearing. By this means as great as possible an electromagnetic coupling between the coils is achieved, as a result of which the signal transfer is better and more reliable.
If, in accordance with a further embodiment, the bearing is made of a nonferrous material, the first and/or second coil can be located in a recess in the first or second part, respectively. In a further embodiment, the first and/or second coil can even be completely embedded in the first or second part, respectively. The non-ferrous metal will, after all, not disturb the magnetic field lines.
According to a further embodiment, the first and/or second coil comprise/comprises printed windings. Electronic circuits connected to the first or the second coil, respectively, can also be incorporated on the first and/or second part of the bearing. The windings and/or electronic circuits can, for example, be produced and applied by thin film techniques known to those skilled in the art. By this means an even more compact construction of the bearing according to the present invention is possible.
When the first and second covering are formed by U-shaped circular members, the at least one air gap is preferably formed by at least one recession in one of the U-shaped circular member legs.
In a second aspect, the present invention also relates to an assembly of at least one bearing according to the present invention and a rotary shaft supported by the at least one bearing, characterized in that the assembly is further provided with an electrical circuit fixed on the rotary shaft, which circuit has connections linked to a second coil.
By this means it is possible to produce an electrical coupling from the stationary part of the bearing via the rotary part of the bearing to a circuit fixed on the rotary shaft, and vice versa.
In one embodiment according to the present invention, signals originating from the circuit are fed to the second coil via a signal line.
Using an assembly according to this embodiment it is therefore possible to make signals originating from the circuit, for example measurement signals, available on the stationary part of the bearing via the second coil and first coil. The signals can then simply be passed on to evaluation or control circuits.
In a further embodiment the first coil is connected to an electrical power supply an the second coil is connected to the circuit via a power line.
By this means it is possible to provide the circuit on the rotary shaft with electric power.
It will be clear to a person skilled in the art that multiple bearings according to the present invention can be used in order both to provide the circuit with electrical power and to make the signals from the circuit available on the stationary part of the bearing. It is also conceivable that, for example, the signals originating from the circuit are multiplexed in the circuit in a manner known to those skilled in the art, by which means more than one signal from the circuit can be transmitted to the stationary part of the bearing.